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EMG (Electromyography)What is it?EMG is short for Electromyography. This is measuring the electrical activity generated by the muscle cells (fibres) as they contract. EMG is often used to describe the instrument used as well as the measurement. The signal is not a constant DC type signal but consists of a range of different frequencies from 20Hz to 10,000 Hz but the greatest levels are from 20 to 1000Hz. These frequencies are important and most instruments can be set to wide band around 20 to 600 or 1000Hz and narrow band 100 to 200Hz. The wide band allows the instrument to measure over 90% of the signal and is ideal if you are trying to relax a muscle or if the muscle is over worked or fatigued. This is because a muscle fatigues the frequencies that the muscle operates in drop lower and may drop below the narrow band giving false results. The narrow band is however very useful for retraining muscles as althrough it cuts out approx. 70% of the muscle signal it also stops most noise and results in a clearer signal. The Instrument used is an Electromyograph. This instrument uses very high gain and low noise amplifiers to increase the microvoltage produced by the muscles into a much higher voltage that can then be used to display and record the signals. The early instruments needed needles inserted into the skin to detect the muscle voltages then with the increasing quality of the electronics used the instruments were able to use electrodes applied to the skin surface. This was a great inprovement and allowed the wider use of the instruments. Even low cost quality instruments now provide good results with surface electrodes. The instruments have 3 leads that connect to electrodes on the skin surface. The measurement is made between the 2 active electrodes and the third electrode acts as a common or ground. The signal from the muscles
This is used to re-train damaged muscles and also to teach people to relax tense muscles. It is used for treating Tension Headaches, RSI(OOS), and Incontinence. How do you use it?An EMG instrument is required to measure the muscle activity. The instruments have three sensors that are held in firm contact with the skin. Two of these sensors detect any signal between them while the third sensor acts as a reference. The two measuring sensors are placed along the muscle group of interest. The instrument will then indicate the activity of the muscle.If the muscle is relaxed then a low value will be indicated. A high level when the muscle should be relaxed indicates the the muscle is being held in tension usually without the person being aware of it. With practice the person can learn to relaxed the muscle and in time will be able to keep it relaxed. Holding muscles in tension is a major cause of tension headache and RSI. When the muscle is tensed the reading should increase with increasing muscle tension. If a muscle is very weak only a small change occurs. Practicing tensing and then relaxing the muscle will strengthen the muscle and with the instrument giving feedback on how the person is doing it acts as positive feedback to keep working. Major uses are the treatment of Incontinence and rehabilation after stroke. Practice with the instrument will greatly improve the muscles functioning. What is it used for?The uses of Muscle biofeedback can be divided in to two main areas;
Muscle StrengthingIt is widely used to retrain muscles after physical damage or surgery. Also used to reteach muscle control after nerve damage and strokes.Biofeedback for the treatment of incontinence is extremely effective. See our page on incontinence for more information. By using this it is possible to retrain the muscles to carry out their proper function. In Anismus the person can learn to relax the muscles at the correct time.
Muscle relaxationIt is used to teach people to relax muscles. This is used for RSI prevention and treatment,Tinnitus, Bruxism, TMJ and Chronic pain.A relaxed muscle should give a reading of 5uV or less, whereas a tense muscle can give up to several hundred uV depending on the size and strength of the muscle. A muscle held in tension will give pain after a period of time. This is the main cause of Repetitive Strain Injury . See our page on Repetitive Strain Injury for more information. What equipment do I need?An EMG is required. These vary from small battery operated models with sound and bargraph Some models offer a digital readout and storage of data. Dual channel instruments with computer interface are also available The Computer interface produces graphs and stores data. They go up to multichannel full computer systems. All provide and adjustable threshold and a number of measuring ranges to cover all muscles, the better instruments have a selectable bandwidth, a wide band (20 to 500Hz) which picks up most muscle activity including that from fatigued muscles but also pick up non muscle activity, and a narrow band (100 to 200Hz) that cuts out most noise but also stops arround 80% of muscle signal.Generally wide band is used for relaxation and narrow band for most other applications.
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